| 摘要 |
PURPOSE: A circuit for sensing a ring signal of a CT(Cordless Telephone) is provided to sense a ring signal by using a cheap transistor instead of an expensive photocoupler on a back end of a bridge diode, thereby reducing cost and size. CONSTITUTION: A ZD(Zener Diode)(100) is abandoned to a local line(15), and removes a noise signal outputted through a bridge diode(25). The first resistor(R1,110) and the second resistor(R2,130) are applied with voltage signals from the bridge diode(25), and distribute the applied voltage signals according to a resistance component ratio. A condenser(C1,120) inputs the voltage signals, and removes or cuts off DC components from the inputted voltage signals. A transistor(140) is applied with the distributed voltage signals in a base terminal, and performs a turn on/off switching process. The third resistor(R3,150) is connected to a collector terminal of the transistor(140) to apply voltage signals outputted from a supply voltage(Vcc), and applies an operation voltage of the transistor(140). The fourth resistor(R4,160) detects a voltage signal outputted by the turn on/off switching process of the transistor(140).
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